Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-06-26
2002-01-15
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069160, C318S571000, C318S572000
Reexamination Certificate
active
06339203
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a main spindle device for a diesink type electric discharge machine which machines a hole shape into a workpiece by positioning an attached tool opposite a workpiece by a certain distance and applying a specific electric discharge voltage between the workpiece and the electrode. More particularly, the present invention relates to a main spindle device in which the main spindle may be controlled both by high speed rotation control and by high precision angle division control.
BACKGROUND OF THE INVENTION
In general, main spindle devices for electric discharge machines are mounted on a machining head, the in and out motion of which is controlled in the plumb (vertical) direction by a servo motor on a column mounted on a bed, with the tool electrode advancing in the depth direction of the hole being machined in the workpiece. The tool electrode is attached at the main spindle device main spindle lower end, and the workpiece is placed on a surface plate on top of a table mounted on the head. A machining vessel placed around the surface plate is filled with a machining fluid which serves as an electric discharge machining medium, and machining of the workpiece is carried out therein in a submerged state.
It is advantageous when machining holes of various shapes using a main spindle device of this type to be able to move the tool electrode not only in and out in the advancing direction, but also to be able to turn the electrode or the workpiece in the high speed mode around the main spindle, or to angle divide in the rotational direction around the center axis of the main spindle. This makes it possible to perform electric discharge machining of machined holes having complex profiles by moving a round rod or other simple shaped tool electrode while rotating it with respect to the workpiece, or to attain a desired angle with respect to the workpiece using a tool electrode formed in a desired shape, such that machining can be performed at a desired angle of inclination. It is also possible, by combining main spindle angle division and perpendicular in and out motion, to machine complex machining holes such as screw holes.
Spindle devices in which such rotation control and angle division control are possible have been utilized for some time, and have been described in the patent literature. We shall now explain an example of a conventional main spindle device representative of such devices. In the explanation below, the motion control axis of the main spindle in the machining depth direction is referred to as the Z axis, the motion control axis in one axis direction on a plane perpendicular to the Z axis is referred to as the X axis, and the motion control axis in another axis direction perpendicular to the X axis on the aforementioned plane is referred to as the Y axis. Further, a rotation at approximately 1,000 rpm, and preferably at approximately 3,000 rpm is referred to as high speed rotation, and the axis rotational direction control is referred to as R axis control. Rotating the main spindle around the main spindle center to precisely position it at a desired angular position is referred to as angle division, and control of the rotational direction thereof in the control is referred to as C axis control. Rotation in that case is of course at a slow speed.
An example of a main spindle device in which the above-described operations are possible is depicted in FIG.
4
. In
FIG. 4
there is a main spindle device main unit
1
; a main spindle
1
A; a machining head
2
; a servo motor
41
; a rotary encoder
42
; and a transfer mechanism
43
which transfers rotation of servo motor
41
to the main spindle. Explanation of the mechanism which moves the machining head
2
in and out, i.e. up and down, in the Z axis direction is omitted.
A rotary encoder
44
is attached to the servo motor
41
and the rotational speed of the servo motor
41
is detected. The rotary encoder
44
detects the rotation of a servo motor, and therefore a rotary encoder resolution of approximately 4,000 divisions (number of increments per degree) is sufficient. The rotary encoder
42
for angle division is attached to the main spindle
1
A on machining head
2
, and the angular position of the main spindle
1
A is detected. The rotary encoder
42
is also variously referred to as the rotary scale and differs from devices normally placed on motors; a device having an extremely high resolution of, for example, 360,000 divisions is used. The reason such extremely high resolution rotary encoders or rotary scales are used is to respond to the particular workpiece requirements of high angle division precision. In particular, in electric discharge machining such as the screw hole machining described above, servo control may performed in which the tool electrode is controlled simultaneously in the Z axis and C axis directions while maintaining a fixed gap between the tool electrode and the workpiece, such that a much higher precision of angle division is required.
The transfer mechanism
43
comprises a coupling
43
A affixed to the servo motor
41
output axis end, a pulley
43
B affixed through the coupling
43
A to the servo motor
41
axial end, a timing belt
43
D running between the pulleys
43
B and
43
C, and a worm wheel
43
F affixed to a machining head
2
. Rotation of the servo motor
41
is transferred to the worm
43
E, which causes the worm wheel
43
F to rotate; the main spindle
1
A is decelerated and rotates by means of the worm wheel
43
F. As will be described below, that deceleration ratio is determined in accordance with the resolutions of the rotary encoders
42
and
44
. Therefore in the case, as above, of a rotary encoder
42
having 360,000 divisions and a rotary encoder
44
having 4,000 divisions, a 1/90 device is selected.
When the main spindle
1
A is rotated in the high speed mode in such a conventional device, a feedback signal from the rotary encoder
44
is used to control the servo motor
41
such that the main spindle rotates at a desired speed. In this situation, no feedback signal from the rotary encoder
42
is used.
Meanwhile, when angle dividing the main spindle
1
A, the motor driver is switched in order to validate the feedback signal from the rotary encoder
42
, which is used to control the angular position of the servo motor
41
, while at the same time the feedback signal from the rotary encoder
44
is used to control the angular position of the servo motor. The reason for using two encoders in this manner is to permit a speed reducer to be interposed between the main spindle
1
A and the servo motor
41
. Due to the small amount of looseness, backlash, clutch slippage, etc. inherent in the speed reducer, control of the servo motor
41
does not immediately match that of the main spindle
1
A, and therefore without feedback control is not stable from the respective rotary encoders for the servo motor
41
and the main spindle.
Feedback control using the two rotary encoders thus requires that the rotary encoder
44
resolution and the rotary encoder
42
resolution be matched. In this conventional example, a speed reduction ratio of 1/90 is selected, so the resolution of the 4,000 division rotary encoder
44
has a converted resolution of 4,000×90=360,000 at the main spindle
1
A.
Another example of a main spindle device in which the above-described operations are possible is depicted in FIG.
5
. Parts which are the same or similar as parts in the example described in
FIG. 4
are given the same reference numerals. This example uses the same technical concept as the main spindle device disclosed in Laid Open Patent JP-H6-134624. In
FIG. 5
, there is depicted a main spindle device main unit
1
; a main spindle
1
A; a spindle
18
which is an integral piece with the main spindle
1
A; a servo motor
51
for angle division; a rotary scale
52
attached around the spindle
18
; and a brake device
54
which holds the main spindle
1
A at an angle position after angle division has been performed. As in th
Nakamura Takahiro
Yamada Kenji
Devinsky Paul
Evans Geoffrey S.
Sodick Co. Ltd.
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